1. Field
Embodiments relate to base-station antennae for use in mobile communication systems.
2. Related Art
Dipole antennae are common in the communications industry, and conventional structures, including half-wavelength dipoles with “bow tie” structures and “butterfly” structures, are described in several known publications.
In particular, panel base-station antennae, such as those used in mobile communication systems, rely heavily on dual polarization antennae. In many cases, these antennae are constructed using single linear polarized elements, grouped in such a way that creates dual polarization. In this case, two separate arrays of radiating elements are required to radiate on both polarizations.
Building antenna using this approach is undesirable, however, because creating the dual polarization effect with single linear polarized elements increases the labor cost and the number of parts involved in the antenna's manufacture, while reducing its overall performance. To overcome this, most dual polarization antennae are made with directly dual polarized elements, either by including a single patch element fed in such a manner as to create a dual polarized structure, or by combining two single linear polarized dipoles into one, thereby making a single, dual polarization element.
Feeding signals to and from these dual polarization structures is usually accomplished by conventional coupling structures such as coaxial cables, microstrip or stripline transmission lines, or slits. The drawback to using these conventional coupling structures with the antennae and dipoles described above is that they increase the number of parts needed to construct the antenna, thereby generating undesired intermodulation distortions.
In addition, manufacturing these panel antennae with dipoles that include numerous radiating elements often requires numerous solder joints and screw connections. The total number of parts required in such panel antennae, in addition to the cost of their assembly, makes them unsuitable for mass-production. In addition, solder, screws, and similar types of attachments between parts not only add to the manufacturing time and labor cost, but also generate undesired intermodulation distortions as well.
In addition to avoiding these intermodulation distortions, it is also desirable to achieve good port-to-port isolation between the two inputs of the radiating elements in the antenna in order to achieve an efficient communication system. This isolation is the measure of the ratio of power leaving one port and entering the other port. But using the air dielectric transmission lines that are common in conventional coupling structures creates distortions in the signal fed to and from the reflector. In these circumstances, it is prohibitively expensive and difficult to achieve the desired isolation, meaning that the antenna cannot be configured such that one port is used for transmission and the other port for reception.
Finally, in addition to having good port-to-port isolation characteristics and a minimum of intermodulation distortions, it is also desirable for the dipoles in the antenna array to have a good impedance so that all of the dipoles in the array can be properly matched.
In conventional antennas (e.g., butter fly design antennas and Four Square dipole elements), regular dipole antennas have issues with cross polarization and isolation between the same band elements and different bands for multi band and higher beam width antennas. Minimizing cross polarization and isolation using conventional techniques are expensive and time consuming. Further, development procedures and production of conventional antennas is expensive.